Citrus Fruit Peeling Process

ABSTRACT

An efficient process for enzymatically peeling citrus fruit applies a vacuum to perforated fruit and, while maintaining that vacuum, introduces an enzyme solution to the perforated fruit. The fruit is infused with the enzyme by releasing the vacuum pressure. After incubating the enzyme, the albedo of the fruit is weakened and the citrus peel can be readily removed. The peeled fruit may be divided into sections and the encompassing membrane removed.

FIELD OF THE INVENTION

This invention concerns an efficient process for peeling citrus fruits.More particularly, the process uses an enzyme to weaken and/or dissolvethe albedo between the citrus peel and the citrus fruit sections whichit surrounds.

BACKGROUND

The process of this invention permits the efficient peeling of citrusfruits so that individual segments of the fruit can be readily prepared.As is well known, citrus fruit has an outer peel and inner fruitsegments separated from one another by membranes that also surround eachindividual segment. Between the outer peel and the membranes surroundingthe individual segments is a white, pithy material known as the albedo.

In the past, citrus peeling has been accomplished by hand peeling theskin and removing the albedo to expose the fruit segments. Typically,the skin peeling and albedo removal has been done with a knife, whichleads to removal and loss of some of the fruit. Complete removal of thealbedo, and its white color; from the fruit segments requires additionalprocessing time and care.

Peeling methods using mechanical equipment of various types is alsoknown to those in the business. Generally, however, such mechanicalpeeling processes leave the peeled fruit in a condition that stillrequires hand removal of some portion of the albedo.

Processes have also been proposed to use an enzyme, such as pectinase,to dissolve and/or weaken the albedo so that the skin can be,removedfrom the segments of meat inside the citrus fruit. For example, U.S.Pat. Nos. 5,170,698 and 5,196,222 to Kirk concern a process and relatedapparatus to peel citrus fruit where the fruit is perforated, given anequatorial cut, and deposited in a canister. The canister is filled withan albedo degrading solution, such as an aqueous solution of commercialpectinase, or a mixture of enzyme solutions. The albedo degradingsolution is vacuum infused into the fruit to substantially disintegratethe albedo of the fruit.

Another peeling process simply removes a strip of citrus outer peelsubstantially at the equator of the fruit. The fruit is immersed in anenzyme solution. Then, a vacuum is applied to remove air from the citrusfruit and released. See, for example, U.S. Pat. No. 5,989,615.

Another possible peeling process involves submerging fruit in a fluidfollowed by the application of a vacuum. The vacuum may be applied inone or two steps. Thereafter, the vacuum is released and pressure isapplied to the fluid. The fluid may contain pectinase. See, U.S. PatentPublication US 2004/0043126.

It has been found, however, that those prior art methods do not functionwell when scaled to commercial operations.

SUMMARY

The process of the present invention prepares citrus fruits by preparingthe fruit for processing by the steps of grading the fruit intosubstantially uniform size ranges or a mix of graded fruit and washingthe fruit to remove surface debris, dirt, residues and naturallyoccurring waxes. A surface active agent may be used in the washing step.The clean, graded fruit is then subjected to a perforating process thatcreates a plurality of holes through the outer peel of the fruit andextending into the albedo inside the outer peel. The perforated fruit isthen rinsed to remove any particle of the outer peel and albedo that mayremain on the fruit.

After rinsing, the fruit is placed in a chamber. After the chamber isclosed, a vacuum is applied to the inside of the chamber and the fruitcontained therein. After a predetermined period of time that allows thepressure inside the fruit to equilibrate with the vacuum, an enzymeeffective to degrade the albedo is introduced into the vacuum chamber.Sufficient enzyme is introduced to cover all the fruit contained in thevacuum chamber.

After the enzyme has been introduced, the vacuum is released and thechamber pressure is vented to atmospheric pressure. The fruit may thenbe subjected to heat and undergoes an incubation process. Heataccelerates the enzyme activity. The enzyme then attacks and breaks-downthe albedo of the fruit pieces. Following incubation, the fruit iscooled, then peeled, and the enzyme is deactivated.

Subsequently, the fruit is rinsed, the outer peel is removed, and theindividual segments are prepared for further processing.

Further details of these, as well as other, steps are discussed in thedetailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

Many objects and advantages of the present invention will be apparent tothose skilled in the art when this description is read in conjunctionwith the appended drawings wherein like reference numerals are appliedto like elements and wherein:

FIG. 1 is a schematic illustration of a citrus fruit;

FIG. 2 is a schematic diagram of process steps according to thisdisclosure;

FIG. 3 is a front view in partial cross section of a fruit perforatingunit of this disclosure;

FIG. 4 is a partial cross-sectional view taken along the line 4-4 ofFIG. 3;

FIG. 5 is a partial cross-sectional view taken along the line 5-5 ofFIG. 4;

FIG. 6 is an enlarged, partial view of a perforation roller used in thefruit perforating unit;

FIG. 7 is an enlarged, partial view of a swing roller used in the fruitperforating unit;

FIG. 8 is a schematic diagram of the enzyme standardization process ofthis disclosure; and

FIG. 9 is a chart of a calibration curve.

DETAILED DESCRIPTION OF THE INVENTION:

In commercial processing of citrus fruit to obtain citrus fruitsegments, large quantities of freshly harvested citrus fruit areprovided to the process. The process of this invention is suitable foruse with citrus fruits including, for example, grapefruit, oranges,lemons, and limes. Depending upon the particular citrus fruit to beprocessed, certain features of the apparatus may require modification,some of which will be discussed below.

Some characteristics of citrus fruit, grapefruit in particular, arehelpful background for this invention. FIG. 1 shows, for example, agrapefruit 10 which has been cut transversely to show its internalstructure. The outside of the grapefruit is a tough, waxy outer peel 12that contains cells with grapefruit essential oils. Toward the center,the grapefruit 10 includes a plurality of fruit sections 14, each ofwhich is surrounded by a membrane 16. Between that membrane 16 and, theouter peel 12 is a pithy white layer 18, also known as the albedo.

The first step in the process involves an initial inspection of theexterior of freshly harvested fruit 10. That inspection step involvesdetermining whether the individual fruits are suitable for the process.To that end, the pieces of fruit are examined to determine suchqualities as firmness, cleanliness, and rotted condition. Rotted fruitis rejected and discarded or used in byproduct process streams. Softfruit is likewise rejected, but may be used in other byproduct processstreams including, for example, juice extraction. Fruit which isexcessively dirty Is pre-washed to an acceptable level for handling inthe process. For quality analysis purposes, a sample of fruit from eachtruckload is examined and a record is made of the percentage portionswhich are too dirty, rotten, or too mushy.

With reference to FIG. 2, the next step involves sizing 20 the fruit sothat the pieces of fruit satisfy minimum size criteria. For example,grapefruit are preferably sized so that the minimum diameter is about3.25 inches, while oranges are preferably sized so that the minimumdiameter is about 2.875 inches. These preferred sizes are selected, inpart, so that the resulting fruit segments have appropriate size forcommercial sale. These preferred minimum diameters may, of course, beselected to have different values depending on the processing equipmentto be used; however, the preferred values expressed are believed to beworkable sizes for commercial operations. Other kinds of citrus fruitthat are typically smaller than oranges and grapefruit, namely lemons orlimes, would be expected to have different, smaller preferred diameters.Fruit which fails to meet the minimum preferred diameter criterion isrejected for the process and passed to other by product streams, suchas, for example, juice extraction. Fruit that successfully passes thesizing operation is temporarily stored in bins that may be fashionedfrom a suitable conventional plastic material.

Next, the bins with appropriately sized fruit are dumped into theprocessing line which a washing step 22 is performed. Washing isaccomplished by advancing the fruit by a suitable conveyor that movesthe fruit through suitable washing apparatus that includes rotatingbrushes that effectively scrub the outer surface of the pieces of fruit.As the fruit progresses through the washing apparatus water is sprayedon the fruit surface to aid the scrubbing operation. In addition, thefruit is sprayed with a suitable surface active agent, e.g., an alkalinedetergent having a concentration of about 14,000 ppm, to further enhancethe scrubbing operation. The scrubbed fruit is then immersed in a weakperacetic acid solution for sanitizing purposes. For example, theperacetic acid with a concentration of 70 ppm may be advantageouslyused.

After sanitization, the fruit is subjected to a skin preparation step24. In this skin preparation step, the outer peel of the grapefruit istreated to enhance access to the albedo by an enzyme solution to beapplied later. This skin preparation step may involve, for example,abrasion of the outer peel or perforation of the outer peel. Othertechniques may also be apparent to those skilled in the art.Nevertheless, the skin preparation step 24 at least partially removessome of the outer peel so that access is provided to the albedo atmultiple locations on the fruit. With the abrasion technique, the outerpeel is scuffed to roughen it and expose parts of the albedo randomlydistributed about the surface of the fruit.

The currently preferred skin preparation technique, however involvesperforation where the outer peel of each fruit is mechanicallypenetrated to produce a plurality of holes. For oranges and grapefruit,mechanical perforation using pins having a length of about 0.1875inches, and a diameter of about 0.0276 inches (about 0.7 mm) has beenfound to be successful. The mechanical perforation step is intended toprovide perforations randomly distributed over at least about 75% of thesurface of each piece of fruit. Preferably, the perforations arerandomly distributed over substantially the entire surface of each pieceof fruit.

Mechanical perforation can be accomplished, for example, using aperforator assembly 30 (see FIG. 3) which includes a housing 32 having apair of ends. One end has an inlet opening sized to simultaneouslyreceive multiple pieces of fruit and an inlet housing 34 that includesan inlet ramp 36 for delivering fruit to the inlet opening. The secondend of the perforator assembly 30 has a discharge opening that deliversperforated fruit to a discharge chute 38.

The perforator assembly 30 also includes an internal screw conveyor 40that is rotatable about its longitudinal axis. The conveyor 40 Includesa generally helical surface extending generally radially outwardly fromthe axis. The helical surface makes a plurality of revolutions about itsaxis between the ends of the housing 32, for example six full revolutionof the helical surface may be provided. The pitch of the helical surfacefor each revolution is selected so that at least one piece of fruit canbe received between axially adjacent parts of the helical surface,although the pitch may be sufficient to accommodate a plurality ofpieces of fruit between such axially adjacent parts of the helicalsurface. To drive the screw conveyor 40, a suitable conventional motor(not shown) may be provided at one end of the conveyor 40. When thescrew conveyor 40 rotates, it mechanically advances fruit from the inletopening at the first end to the discharge opening at the second end.

A plurality of parallel, generally cylindrical, elongated rollers 42,42′ (see FIG. 4) support the fruit as It moves through the perforatorassembly 30. By way of example, as many as ten such rollers may be used.Preferably, the rollers 42, 42′ are uniformly spaced from one anotheralong an arc (see FIG. 5) that is centered on the axis of the screwconveyor 40. In this manner the minimum spacing between the edge of thescrew conveyor 40 and the roller is substantially the same for eachroller 42, 42′. Each roller 42, 42′ is rotatably mounted in theperforator assembly 30 so as to be rotatable about its longitudinalaxis. Suitable conventional motors 44, 46 are provided to rotate therollers 42, 42′ and are drivingly connected to the rollers 42, 42′ witha conventional drive mechanism. The motor 44 drives the rollers 42,while the motor 46 drives the rollers 42′ on the other side of theperforator assembly 30.

The rollers 42, 42′ preferably comprise a plurality of pin rollers 50with a swing roller 48 disposed between pairs of pin rollers 50. As bestseen in FIG. 6, the surface of each pin roller 42 includes amultiplicity of perforator pins 44. These pins 44 may be arranged inlongitudinal rows, as shown, or in any other desired pattern. The pins44 are sized to provide the desired perforations for the fruit beingprocessed. The pins 44 may be cylindrical or non-cylindrical and mayinclude a blunt wire tip. When processing grapefruit and/or oranges,pins having a diameter of about 0.0275 inches (0.7 mm) and a length ofabout 0.1875 inches have been found to be suitable. Moreover, the pins44 are spaced from one another so that the weight of the fruit willcause the fruit to be impaled by the pins but the pins are not soclosely spaced that the fruit is supported by so many pins 44 that thefruit is not effectively impaled.

Each swing roller 58 (see FIG. 7) includes a generally helical surfaceelement 52 that extends along substantially its entire length. Thehelical surface element 52 may be a surface attachment as shown, or maybe a groove (not shown), or a combination of both. As the swing roller58 rotates, the helical surface element 52 tends to push the pieces offruit laterally with respect to the axis of the screw conveyor 40. Toaccomplish this action where the screw conveyor 40 rotates in acounterclockwise direction (looking downstream from the inlet 36), theswing rollers 48 (see FIG. 4) on the right side rotate clockwise andhave a right-handed helical surface element 52. Conversely, the swingrollers 48′ on the left side rotate counterclockwise and have aleft-handed helical surface element 52′.

As the fruit enters the perforator assembly 30 (see FIG. 3) from theinlet opening, the screw conveyor 40 advances the individual pieces offruit toward the discharge chute 38. Although the precise interactionbetween the rollers 42, 42′, the screw conveyor 40, and the individualpieces of fruit is not fully understood and characterized, the swingrollers 48′ and associated pini rollers 50 on the left side tends topush fruit laterally to the left of the screw conveyor axis, while theswing rollers 48 and associated pin rollers 50 on the right side tendsto push fruit laterally to the right of the screw conveyor axis.Interaction between the screw conveyor 40 and the fruit tends to rotatethe fruit about an axis extending substantially radially from the axisof the screw conveyor 40. The pins 44 of the rollers 50 puncture theouter peel of the fruit as the rollers themselves rotate. That rotationof the rollers 50 tends to cause the fruit to also rotate about a secondaxis substantially parallel to the axis of the rollers 50 and the axisof the screw conveyor 40. Action of the helical surface elements of theswing roller 48, 48′ tends to cause the fruit to rotate about a thirdaxis substantially perpendicular to the axis of the screw conveyor 40.Accordingly, as the fruit moves through the perforator assembly 30, itis subjected to rotation about multiple axes so that virtually theentire surface of the fruit is exposed to the pins 44 and perforated bythem.

Fruit discharged from the discharge chute 38 of the perforator assembly30 may be collected in, for example, a container such as a large,reusable basket. Moreover, the fruit discharged from the perforatorassembly 30 is periodically inspected to determine what portion of thefruit surface has been effectively perforated. If about 75% or less ofthe surface is effectively perforated, the volume of fruit fed to theinlet of the perforator assembly 30 is reduced. Moreover, at apredetermined time interval, for example once about every 30 minutes, apiece of fruit Is subjected to vacuum, and then submerged in coloredwater. Based on the resulting coloring of the outer peel, the uniformityof the perforation step can be assessed and recorded for process controlpurposes.

After the perforation step is completed (FIG. 2) the fruit is rinsed 54to remove any particles of citrus peel that may adhere to the surface ofthe fruit.

Next, the containers of fruit are deposited in a vacuum chamber. Thevacuum chamber used for this process is large, and may have dimensionsof about ten feet in length, about four feet in width, and a depth ofabout four feet. The depth, if desired, may also be as great as aboutten feet; however, the depth must be selected such that the bottom-mostfruit in the chamber are not crushed by the weight of fruit above it inthe chamber. To provide substantially continuous movement of fruitthrough the process, a pair of vacuum chambers may be used. In such anarrangement, fruit can be loaded into an open vacuum chamber whileoperations proceed in the second vacuum chamber. Then, when operationsin the second vacuum chamber are finished, the first vacuum chamber canbe closed and vacuum operation proceed therein while the second vacuumchamber is emptied and loaded with fruit.

With the fruit in the vacuum chamber and the chamber closed, a vacuum 56is applied to the interior of the vacuum chamber. The vacuum in thechamber preferably likes in the range of about 1 to about 29 inches ofmercury (In. Hg), and most preferably is about 27 in. Hg. This vacuumlevel is maintained in the vacuum chamber for an initial period of about1 second to about 2 hours, and preferably for about 7 minutes. Theprecise amount of time for the vacuum step depends upon the amount offruit which must be processed and the level of vacuum desired. Forexample, if fruit must be processed substantially continuously, a shorttime at a high vacuum may be appropriate; whereas, a small occasionaloperation may proceed in occasional batches so a long time at a lowervacuum may be acceptable.

Separately from the movement of fruit, an enzyme solution is prepared58. The enzyme solution includes pectinase and water, with the pectinaseconcentration preferably being in the range of about 0.01% to about40.00%. The percentages are weight percentages. The particularpercentage used will depend upon the particular enzyme being used. Amongthe preferred enzymes for this process are Novozyme (Novoshape KE545005) from Novo and Crystalzyme PML-MX from Valley Research. Aconcentration of about 0.15% is suitable for those preferred enzymes.When prepared, the temperature of the enzyme solution is preferablymaintained in the range above freezing to less than the denaturingtemperature of the enzyme, preferably in the range of greater than 32°F. to about 130° F., and most preferably about 70° F. The particulartemperature selected from this temperature range is also picked so as tobe below the deactivation (denaturation) temperature for the enzyme.

With the enzyme solution prepared 58 and fruit in the vacuum chamberunder a vacuum condition, the enzyme solution is transferred 60 into thevacuum chamber while the vacuum is maintained. For example, thistransfer 60 into the vacuum chamber may be accomplished by appropriatevalves which allow the enzyme solution to enter the vacuum chamber fromthe bottom. The enzyme solution is applied to the vacuum chamber untilall the fruit in the chamber is covered by the solution. By covering thefruit with a perforated lid when the fruit is loaded into the vacuumchamber, any tendency of the fruit to float above the enzyme solution issubstantially avoided. This transfer step 60 preferably takes place overa time period of about 1 to about 120 minutes preferably about 1 toabout 10 minutes, and most preferably about 3 minutes.

Generally speaking, the known processes for enzymatic treatment ofcitrus fruit involve batch processing at least at the process pointwhere enzymatic treatment occurs. When earlier processes for enzymatictreatment of citrus fruit have been scaled from laboratory-scale tocommercial scale, the process performance has not been uniform as to thevarious pieces of fruit in each batch. On a commercial level, theenzymatic treatment can occur in tanks that are, for example, 10 feetlong by 4 feet wide and 4 to 10 feet deep. While the exact reasons forsuch lack of uniform processing are not fully known, deep tanks filledwith enzymatically active liquid have a hydrostatic pressure gradientthat increases from the top of the tank to the bottom of the tank. Thathydrostatic pressure gradient opposes any vacuum that may be applied tothe head space at the top of the tank and appears to counteract theeffect of the vacuum on the perforated fruit. In addition to thathydrostatic effect, surface tension resistance to formation of airbubbles escaping from perforations, as well as resistance air flowthrough the long channel formed by the perforation step, resist releaseof gas from inside the fruit when bathed in liquid.

The sequence of steps in applying the enzyme to the perforated fruit isbelieved to be very important. While the precise mechanisms are not yetfully understood, it appears that applying the vacuum to the perforatedfruit prior to submerging fruit in the enzyme solution allows any airand/or other gas inside the fruit to be substantially uniformly andconsistently vented to the vacuum chamber with minimal resistance and tofacilitate enzyme penetration. Moreover, any hydrostatic effects andsurface tension effects are effectively eliminated because no gas/liquidinterface exists during the vacuum process. Rather, the prolonged vacuumin the chamber outside the fruit establishes a pressure differential sothat air and or gas inside the fruit vents to the lower pressure of thevacuum chamber until the pressure inside the fruit essentiallyequilibrates with the vacuum pressure outside the fruit.

The vacuum in the chamber is then released. Upon release of the vacuum,the enzyme solution enters the perforations in the outer peel of thefruit and, thus, has access to the albedo of the fruit. About 30% of theenzyme solution in the chamber is absorbed by or infused into theperforated fruit. That portion of the enzyme solution that is notabsorbed by the fruit is drained 62 from the vacuum chamber for use in asubsequent batch of fruit. Before the enzyme solution drained from thevacuum tank is used for another batch of fruit, however, severaladditional steps occur. Periodically, the drained enzyme is analyzed sothat the enzyme concentration can be standardized 64. Thatstandardization process may occur as frequently as once for each batchof fruit; but, the standardization process may occur less frequently,such as once for every two to four batches. Based on the standardizationprocess, substantially pure enzyme additions may be made to replenishthe enzyme solution and return its enzyme concentration to the targetconcentration. The technique for this standardization process is animportant part of this invention and is discussed separately below.

After each application of enzyme solution 60 to the vacuum chamber, theenzyme solution drained from a previous batch is topped-up or topped-off66 to replace enzyme absorbed by the previous batch. To top-off 66,fresh enzyme solution at the target enzyme concentration is used, e.g.,at 0.15% concentration using the most preferred enzyme concentrationdiscussed above.

The enzymatically treated fruit is then placed in an incubation bath 62for an incubation period ranging from about 5 to about 120 minutes,preferably from about 15 to about 60 minutes, and most preferably about45 minutes. The incubation bath preferably is water (but it may includeenzyme) at a temperature in the range from about freezing to less thanthe denaturing temperature for the enzyme being used, preferably in therange of greater than about 32° F. to about 155° F., more preferably inthe range of about 100° F. to about 150° F., and most preferably about122° F. (50° C.). The temperature may preferably be selected in thoseranges such that the enzyme has maximum activity per unit substrate.During the incubation period, the enzyme attacks the albedo between thefruit outer peel and the albedo from the membrane surrounding the fruit,substantially destroys the albedo thereby loosening the outer peel fromthe membrane surrounding the fruit, and substantially avoiding asubsequent need for further removal of the albedo.

After the incubation step 62, the fruit is cooled 64. Cooling can beeffected by allowing the fruit to equilibrate with room temperature.Alternatively, cooling can be accomplished by immersing the fruit incold water for a time sufficient to reduce the external temperature ofthe fruit to a level where it can be handled.

With the fruit cooled, it is peeled 66. That peeling step can be done byhand or mechanically, although it is preferred that hand peeling beused. During the hand peeling step, any residual albedo can be scrapedfrom the membrane covered segments.

After the fruit has been peeled, the enzyme is deactivated 68.Deactivation of the enzyme is effected by placing the fruit in a waterbath or otherwise heating it to a temperature at or above the denaturingtemperature. Suitable deactivation temperature lies in the range ofabout 100° F. to about 280° F., more preferably in the range of 170° F.to about 200° F., and most preferably about 194° F. (90° C.) for adeactivation time in the range of about 1 second to about 3 hours, mostpreferably about 15 seconds. Deactivation techniques other than heatingmay also be used. For example, enzyme deactivation may be accomplishedusing an unfavorable environment, such as an acidic. environment, abasic environment, or a pressure environment. Yet another enzymedeactiviation technique may be a chemical deactivation.

After enzyme deactivation, the peeled fruit is rinsed 70, and the fruitis then separated into segments 72. If desired, the Membrane surroundingthe fruit segments may be removed so that only the meat of the citrussections remains.

The process of this invention generates high quality, substantiallyuniform, and consistent enzymatically peeled citrus fruit segmentsand/or sections that can be further packaged for retail sale andconsumption. Moreover, the process allows commercial scale use of enzymepeeling of citrus fruit.

As noted above, the foregoing process may be used for high throughputsof fruit such that the process is substantially continuous even thoughsteps such as the vacuum chamber operation take place batchwise. Wherethe vacuum treatment step 56 occurs for short time intervals, e.g.,under 30 minutes, the enzyme standardization step 64 must beaccomplished rapidly. Past experience with techniques for determinationof enzyme concentration and activity indicate that special reagents andas much as a day may be required to accurately evaluate enzymeconcentration, particularly when the enzyme concentration is quitesmall. Such time periods are impractical if the enzyme concentrationmust be evaluated in a time frame measured in minutes.

A procedure that allows enzyme standardization in a time frame measuredin minutes begins by preparing a standard substrate 100 (see FIG. 8) ofthe material on which the enzyme acts. For example, when using apectinase, a standard substrate may be prepared by dispersing 2-10%pectin mixture in distilled water along with a preservative andsufficient acid to activate the preservative without having asignificant affect on pH of the solution. The quantity of pectin mixtureused is selected such that the amount of pectin will exceed the amountof pectin that would be destroyed by the enzyme used. The pectin mixturemay preferably comprise 50% low methoxy pectin and 50% high methoxypectin. The preservative may, for example comprise 50% sodium benzoateand 50% potassium sorbate. With that preservative, citric acid may beused. That substrate solution is boiled to completely hydrate thepectin. The thickened substrate solution is then cooled and may bestored at ambient temperature. When cooled, the substrate can be storedas long as six months.

A series of enzyme solutions each having a known enzyme concentration102 is then prepared. The known concentrations range from 0% at thelower end to a value exceeding the nominal enzyme concentration, i.e.bracketing the nominal enzyme concentration. For the most preferredexample discussed herein, the nominal or target enzyme concentration is0.15%, so a concentration range from 0% to 0.20% in increments of 0.01%may be used.

Each of the known enzyme solutions is then mixed with a standard volumeof the standard substrate. For example, 20 ml of each solution may bemixed with 330 g. of the standard substrate. Viscosity is then measured104 for each mixture of a known enzyme solution with the standardsubstrate. Viscosity may be measured, for example, using a BrookfieldLRV viscometer with a #2 Spindle operating at a speed of 60 rpm, andtaking the measurement after 5 minutes.

Viscosities for the known enzyme concentrations may then be plotted tocreate a calibration curve 106. An example of a calibration curve isshown in FIG. 9, where the abscissa 120 is the viscosity and theordinate 122 is the enzyme concentration. The data points of thecalibration curve may be statistically analyzed to provide the bestcurve fit. The nominal or target enzyme concentration 124 is less thanthe highest standard enzyme concentration 126 so that the range of knownconcentrations (and the associated viscosities) will bracket the nominalenzyme concentration 124 and its nominal viscosity 128. It will be notedfrom FIG. 9 that the calibration curve is linear for low concentrations.At higher concentrations, the calibration curve may be nonlinear.

To evaluate the enzyme concentration of the solution drained from thevacuum chamber 64 (see FIG. 2), a sample of the solution 108 (see FIG.8) is taken, e.g., 20 ml. That sample is then mixed 110 with a standardamount (e.g., 330 g.) of the standard substrate. Using the sameBrookfield viscometer with the same spindle and speed, viscosity of theenzyme sample is determined 112, again after 5 minutes. To be sure thatthe measured viscosity of the unknown sample is accurate, a 20 ml sampleof distilled water may also be mixed with the standard amount of thestandard substrate and be subjected to the same viscosity determination,That viscosity sample using distilled water will determine whether anyadjustment of the measured viscosity for the unknown sample needs to bemade.

The measured viscosity for the unknown sample is compared 114 to thecalibration curve (FIG. 9) to determine its enzyme concentration. Forexample, knowing the viscosity 130 of the unknown sample, thecalibration curve graphically provides the corresponding enzymeconcentration 132 Knowing the enzyme concentration of the sample, thequantity of pure enzyme required to raise the level of enzymeconcentration to the nominal level can be determined 116. in any ofseveral ways. For example, a table can be conveniently prepared tospecify the amount of enzyme required for a convenient quantity, e.g.,1000 pounds of solution, as a function of the measured enzymeconcentration in the sample. Alternatively, a graphical correlationbetween enzyme concentration and required pure enzyme could be used.Other techniques, including without limitation use of a programmablecomputer using commercially available programs, can also be used todetermine the required pure enzyme. Moreover, a programmable computerusing commercially available programs could also be used to house thecalibration data, determine the best curve fit, evaluate the unknownenzyme concentration based on its viscosity, and determine the amount ofpure enzyme required for either (i) a predetermined unit of enzymesolution (e.g., 1000 pounds) or (ii) the actual weight of enzymesolution drained from the vacuum chamber.

Regardless of the specific technique used to determine the requiredamount of pure enzyme, by adding the thus determined quantity of pureenzyme to the drained solution, the solution is fortified and its enzymeconcentration is returned to the nominal concentration. Any additionalvolume required to fill the vacuum chamber can then be provided usingfresh, nominal enzyme concentration solution.

This procedure allows the enzyme concentration of the drained liquid tobe evaluated in minutes, rather than hours. Moreover, the procedure iswell suited to rapid batch type processes such as the use of alternatingvacuum chambers as described above.

This enzyme treatment process also digests the outer peel's cell wallsand facilitates the release of grapefruit oil. For sufficiently largevolumes of fruit throughput, the waste, i.e., outer peel and albedo, maybe further processed to produce essential citrus oil.

Using the process described above, a batch of enzyme solution can berecycled, replenished with additional fresh solution, and fortified withpure enzyme to maintain its nominal standard concentration level.Moreover, the standardization process described permits the same enzymesolution to be used as many as 10 to 20 consecutive times before beingdiscarded. Filtration of the drained enzyme solution is an enhancementthat may further increase the useful life of a batch of enzyme solution.

A further enhancement of the process is the addition of a surfactant toenhance the enzyme performance. The surfactant is a surface activeagent, such as a food-grade detergent, which lowers surface tension inthe enzyme solution and makes the cells more recipient to the enzyme.

Throughout this specification certain numerical values have beenidentified and introduced by the word “about”, “essentially”, and thelike. Those numerical values are not intended to be limited to theprecise values stated, but are intended to include variations within 5%above and/or below the specific figure used, as the context may suggest.

It will now be apparent to those skilled in the art that a new, useful,nonobvious process for peeling citrus fruit has been disclosed.Moreover, it will be apparent to those skilled in the art that numerousmodifications, variations, substitutions and equivalents exist forfeatures of the invention that do not materially depart from the spiritand scope of the invention, as defined by the appended claims.Accordingly, it is expressly intended that all such modifications,variations, substitutions, and equivalents which fall within the spiritand scope of the appended claims be embraced thereby.

1-29. (canceled)
 30. A method of determining the unknown concentrationof a known enzyme having a nominal concentration and effective against aknown substrate comprising the steps of: determining a concentrationtest range extending above and below the nominal concentration;determining a plurality of test concentrations in the concentration testrange from a minimum value to a maximum value; preparing a correspondingplurality of standard samples, each having one of the plurality of testconcentrations; preparing a substrate solution containing the knownsubstrate at a concentration exceeding the concentration at which thesubstrate could be consumed by the enzyme of the standard sample havingthe maximum value; mixing a fixed quantity of the each standard samplewith a fixed quantity of the substrate solution; determining theviscosity of each standard sample mixed with the substrate testsolution; correlating the viscosities and enzyme concentration forstandard samples; selecting a sample of an enzyme solution with unknownconcentration; mixing a quantity of the sample corresponding to thefixed quantity of the standard sample with the substrate solution alsohaving the fixed quantity; determining viscosity of the sample; andcomparing the sample viscosity to the correlation of the viscosities andconcentrations for the standard samples to determine the enzymeconcentration of the sample.
 31. The method of determining the unknownconcentration of a known enzyme of claim 30, wherein the known enzyme isa pectinase; and the substrate is pectin.
 32. The method of determiningthe unknown concentration of a known enzyme of claim 30, wherein thenominal concentration is less than about 1% by weight.
 33. The method ofdetermining the unknown concentration of a known enzyme of claim 30,wherein the nominal concentration is about 0.15% by weight.
 34. Themethod of determining the unknown concentration of a known enzyme ofclaim 30, wherein the correlation of viscosities and knownconcentrations comprises a calibration curve.